This was never my favourite Little Britain sketch, where David Walliams bashes moronically into a keyboard before repeating that tired catchphrase. But it turns out it could have been set in any Jobcentre Plus office where staff decide whether 40,000 or so people who apply every month for the new Employment and Support Allowance are successful or not.

If not, they go on the lower Jobseeker's Allowance, losing between £1,349 and £1,633 a year, and are expected to find a job.

Most people would support the idea of helping those who can work to work. But the problem with these assessments is that far too many get it wrong.

Out of 209,200 "fit to work" decisions made in two years, 69,500 have been appealed (or 33%). Of these appeals, 27,500 (40%) have been successful. Overall, more than one in eight refusals were made in error. A new report by Professor Malcolm Harrington published this week has tried to explain why.

Applicants first fill in a 28-page form, before attending a medical assessment organised by Atos Origin, a private firm paid £100m a year by the Department of Work and Pensions to do the job.

Atos in turn hires "health care professionals" - doctors, mainly - to do the medicals and they are expected to spend between 46 and 49 minutes with each claimant. Some doctors "felt constrained by these targets when interviewing complex cases", Harrington found.

These doctors "must complete a large number of assessments in a short time and can too easily rely upon the computer based questions to guide their assessment rather than focusing on the individual".

He added: "A sizable number of reports are produced which do not reflect a claimant's recollection of the discussions that took place."

One example. Claimants are scored by their ability to do certain tasks but there's little flexibility. Mr A told his assessor that he was able to perform a particular task but that it caused pain and fatigue that lasted for hours afterwards. He was found fit to work and requested a copy of the report. He found: "It made no mention at all of the fact I found the tasks difficult to perform, that they caused me pain or that to repeat the task would be near impossible."

In theory, the Atos report is just one piece of evidence, but in practice is taken as gospel in 98% of decisions made.

Harrington found "many Decision Makers lack the confidence to make a decision that deviates from the Atos advice", partly due to training but also because of "the lack of time Decision Makers are allowed to devote to particular cases".

"It's difficult. I mean, they're a doctor," said one. "They've assessed the person, I don't know enough about it to overrule what they're saying."

The Atos doctors, meanwhile, think they're just giving advice.

"These two viewpoints mean that effectively, both parties expect that the other has responsibility for making the decisions," found Harrington. "There is what can be termed a decision gap, which can leave no-one actually claiming responsibility for the benefit decision."

"Computer said no," basically.

There is a "reconsideration" process but this is rarely used. So a third of all cases go to appeal where many are overturned, wasting time and money, the two things the whole system was supposed to save in the first place.

As if it wasn't bonkers enough, Harrington found that: "In a few isolated cases ... people who had been found fit for work were being told they could not claim Jobseeker's Allowance because they were too ill."